They retired that night with high hopes that the morning would bring good fortune. During the last few hours they had had an uneasy feeling that their efforts to find the region of sand were in vain. The next day they were off early, after a hurried breakfast. "We'll get out of these rocks some time this morning," predicted Mr. Lewis with a smile. And he was right. Gradually the boulders they passed grew smaller and the soil more loose. By the time they had stopped for the noon meal they were again among sand dunes. The heat was now terrific. If it had been warm before, it was scorching now. Everywhere they went they were under the blaze of the fierce sun. How the camels managed to keep from burning their feet was a mystery to the youths. Their throats were parched, their tongues numb. Water, water! If they could only drink and drink and drink! But only small amounts were allowed to be taken, for this region was many, many miles across, and there was no well or oasis anywhere near their path of traveling. "If we have much more of this I'm afraid I'll fall off my camel," said Bob with a grim smile. "Not quite that bad off, are you?" laughed Dr. Kirshner. "Dying of thirst is a rare occurrence in this part of the Sahara. But it does happen sometimes, and it is a tragic death indeed." "Worst thing is," explained Mr. Holton, "there is a time when the victim of thirst would die should he touch water. In that case, water is virtually a poison." The sand hills that they were passing over were much lower than those in the country below Wargla. The desert stretched away to the horizon in endless waves, which, as far as the travelers could see, were unbroken. Vegetation was scarce, only a scattering of yellow plants dotting the dunes. This promised to be a disadvantage to the dromedaries, for previously they had occasionally nibbled on the trees and shrubs that were clustered about. "Look at the sky," said Joe, turning his gaze upward. "Funny color, isn't it?" Bob returned. Then, as he peered into the distance, he uttered an exclamation of surprise and fear. But the others had seen also and were equally as excited. Away to their right a heavy mist had risen and was rapidly turning reddish. "A sandstorm!" cried Fekmah in great anxiety. "A sandstorm is coming!" CHAPTER XVII Moments of Horror The explorers, particularly Tishmak, knew the danger of a sandstorm. It was not infrequent for large caravans to be completely engulfed by the heavy veil of sand, leaving only the dead bodies of the camels and their riders. The Americans remembered a tale that Fekmah had told them about a trading caravan of five hundred dromedaries coming to a tragic end in this region. Would their little caravan also perish? "Get your goggles," commanded Fekmah, his tone indicating that he was calm even in the face of danger. "And be sure they fit tightly!" warned Dr. Kirshner. "Even then we'll get some of the sand."